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Leong, S.-l. L., Lantz, H., Pettersson, O. V., Frisvad, J. C., Thrane, U., Heipieper, H. J., . . . Schnürer, J. (2015). Genome and physiology of the ascomycete filamentous fungus Xeromyces bisporus, the most xerophilic organism isolated to date. Environmental Microbiology, 17(2), 496-513
Open this publication in new window or tab >>Genome and physiology of the ascomycete filamentous fungus Xeromyces bisporus, the most xerophilic organism isolated to date
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2015 (English)In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 17, no 2, p. 496-513Article in journal (Refereed) Published
Abstract [en]

Xeromyces bisporus can grow on sugary substrates down to 0.61, an extremely low water activity. Its genome size is approximately 22Mb. Gene clusters encoding for secondary metabolites were conspicuously absent; secondary metabolites were not detected experimentally. Thus, in its dry' but nutrient-rich environment, X.bisporus appears to have relinquished abilities for combative interactions. Elements to sense/signal osmotic stress, e.g. HogA pathway, were present in X.bisporus. However, transcriptomes at optimal (approximate to 0.89) versus low a(w) (0.68) revealed differential expression of only a few stress-related genes; among these, certain (not all) steps for glycerol synthesis were upregulated. Xeromyces bisporus increased glycerol production during hypo- and hyper-osmotic stress, and much of its wet weight comprised water and rinsable solutes; leaked solutes may form a protective slime. Xeromyces bisporus and other food-borne moulds increased membrane fatty acid saturation as water activity decreased. Such modifications did not appear to be transcriptionally regulated in X.bisporus; however, genes modulating sterols, phospholipids and the cell wall were differentially expressed. Xeromyces bisporus was previously proposed to be a chaophile', preferring solutes that disorder biomolecular structures. Both X.bisporus and the closely related xerophile, Xerochrysium xerophilum, with low membrane unsaturation indices, could represent a phylogenetic cluster of chaophiles'.

Place, publisher, year, edition, pages
Hoboken, USA: Wiley-Blackwell, 2015
National Category
Microbiology
Identifiers
urn:nbn:se:oru:diva-52197 (URN)10.1111/1462-2920.12596 (DOI)000350546200016 ()25142400 (PubMedID)2-s2.0-84923646778 (Scopus ID)
Note

Funding Agencies:

Swedish Research Council Formas 

Carl Tryggers Foundation for Scientific Research 

Faculty of Natural Resources and Agricultural Sciences, Swedish University of Agricultural Sciences

Knut and Alice Wallenberg Foundation 

Swedish National Infrastructure for Computing 

Available from: 2016-09-16 Created: 2016-09-15 Last updated: 2017-11-21Bibliographically approved
Båth, K., Persson, K. N., Schnürer, J. & Leong, S.-l. L. (2012). Microbiota of an unpasteurised cellar-stored goat cheese from northern Sweden. Agricultural and Food Science, 21(2), 197-203
Open this publication in new window or tab >>Microbiota of an unpasteurised cellar-stored goat cheese from northern Sweden
2012 (English)In: Agricultural and Food Science, ISSN 1459-6067, E-ISSN 1795-1895, Vol. 21, no 2, p. 197-203Article in journal (Refereed) Published
Abstract [en]

This qualitative study reports on lactic acid bacteria (LAB), yeasts and moulds isolated from three artisanal Swedish cellar-stored goat cheeses aged for 1, 3 and 5 months. Starter culture LAB dominated in the younger cheeses, and Leuconostoc pseudomesenteroides, common in raw goats' milk, had persisted from the unpasteurised milk into all the cheeses. Non-starter LAB dominated in the 5 month cheese, in particular, Lactobacillus sakei, a meat-associated LAB not previously isolated from cheese. Debaryomyces hansenii, and Penicillium and Mucor species were dominant among the yeasts and moulds, respectively. The cheese rind was not formed primarily from Penicillium species as in traditional cheeses such as Camembert - rather, mycelium from Mucor mucedo contributed to rind formation. Mould species known to produce sterigmatocystin, aflatoxins or ochratoxin A in cheese were not isolated in this study; growth of mycotoxigenic Aspergilli may have been inhibited by the cool conditions in the earth-cellar (4-6 degrees C).

Place, publisher, year, edition, pages
Helsinki, Finland: M T T / Agrifood Research Finland, 2012
Keywords
Maturation, lactic acid bacteria, yeasts, moulds
National Category
Food Science Microbiology
Identifiers
urn:nbn:se:oru:diva-52199 (URN)000304917300010 ()2-s2.0-84870547227 (Scopus ID)
Available from: 2016-09-21 Created: 2016-09-15 Last updated: 2018-05-14Bibliographically approved
Pettersson, O. V., Leong, S.-l. L., Lantz, H., Rice, T., Dijksterhuis, J., Houbraken, J., . . . Schnürer, J. (2011). Phylogeny and intraspecific variation of the extreme xerophile, Xeromyces bisporus. Fungal Biology, 115(11), 1100-1111
Open this publication in new window or tab >>Phylogeny and intraspecific variation of the extreme xerophile, Xeromyces bisporus
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2011 (English)In: Fungal Biology, ISSN 1878-6146, E-ISSN 1878-6162, Vol. 115, no 11, p. 1100-1111Article in journal (Refereed) Published
Abstract [en]

The filamentous ascomycete Xeromyces bisporus is an extreme xerophile able to grow down to a water activity of 0.62. We have inferred the phylogenetic position of Xeromyces in relation to other xerophilic and xerotolerant fungi in the order Eurotiales. Using nrDNA and betatubulin sequences, we show that it is more closely related to the xerophilic food-borne species of the genus Chrysosporium, than to the genus Monascus. The taxonomy of X. bisporus and Monascus is discussed. Based on physiological, morphological, and phylogenetic distinctiveness, we suggest that Xeromyces should be retained as a separate genus.

Place, publisher, year, edition, pages
Oxon, United Kingdom: Elsevier, 2011
Keywords
Chrysosporium, Eurotiales, Fungi, Monascus, Phylogeny, Xeromyces bisporus, Xerophile
National Category
Botany
Identifiers
urn:nbn:se:oru:diva-52201 (URN)10.1016/j.funbio.2011.06.012 (DOI)000297873100002 ()22036289 (PubMedID)2-s2.0-80955158588 (Scopus ID)
Note

Funding Agencies:

Faculty of Science and Agriculture 

Swedish University of Agricultural Sciences

Carl-Tryggers Foundation

Available from: 2016-09-15 Created: 2016-09-15 Last updated: 2017-11-21Bibliographically approved
Leong, S.-l. L., Pettersson, O. V., Rice, T., Hocking, A. D. & Schnürer, J. (2011). The extreme xerophilic mould Xeromyces bisporus: Growth and competition at various water activities. International Journal of Food Microbiology, 145(1), 57-63
Open this publication in new window or tab >>The extreme xerophilic mould Xeromyces bisporus: Growth and competition at various water activities
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2011 (English)In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no 1, p. 57-63Article in journal (Refereed) Published
Abstract [en]

Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (a(w)) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X. bisporus were assessed at 20, 25, 30 and 37 degrees C on solid agar media containing a mixture of glucose and fructose to reduce a(w) to 0.94, 0.88, 0.84, 0.80, 0.76 and 0.66. Growth rates of xerophilic species closely related to X. bisporus, viz. Chrysosporium Mops, C. xerophilum and Monascus eremophilus, were also assessed. Optimal conditions for growth of both X. bisporus strains were approx. 0.84 a(w) and 30 degrees C, despite FRR 2347 growing two- to five-fold faster than CBS 185.75. X. bisporus FRR 2347 even grew well at 0.66 a(w) (0.48 mm/day). C. Mops and C xerophilurn were more tolerant of high a(w) than X. bisporus. and could be differentiated from each other based on: the faster growth of C. xerophilum; its preference for temperatures >= 30 degrees C and a(w) >= 0.94 (c.f. <= 25 degrees C and similar to 0.88 a(w) for C Mops); and its ability to grow at 0.66 a(w), which is the lowest a(w) reported to date for this species. M. eremophilus grew slowly (max. 0.4 mm/day) even in its optimal conditions of similar to 0.88 a(w) and 25 degrees C. To investigate the competitive characteristics of X. bisporus at low a(w), both X. bisporus strains were grown in dual-culture with xerotolerant species Aspergillus flavus and Penicillium roqueforti, and xerophilic species A. penicillioides, C. Mops, C. xerophilum and Eurotium chevalieri, on glucose-fructose agar plates at 0.94, 0.84, 0.80 and 0.76 a(w) and at 25 degrees C. Growth rates and types of interactions were assessed. Excretion of inhibitory substances acting over a long-range was not observed by any species; inhibitors acting over a short-range that temporarily slowed competitors' growth or produced a protective zone around the colony were occasionally observed for A. penicillioides, C. Mops and C. xerophilum. Instead, rapid growth relative to the competitor was the most common means of dominance. The xerotolerant species. A. flavus and P. roqueforti were dominant over X. bisporus at 0.94 a(w). E. chevalieri was often dominant due to its rapid growth over the entire a(w) range. At a(w) < 0.80, X. bisporus was competitive because it grew faster than the other species examined. This supports the concept that its ideal environmental niche is sugary foods with low a(w).

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2011
Keywords
Xerophilic, Intermediate moisture foods
National Category
Microbiology
Identifiers
urn:nbn:se:oru:diva-52204 (URN)10.1016/j.ijfoodmicro.2010.11.025 (DOI)000288731100008 ()21145608 (PubMedID)2-s2.0-78651302975 (Scopus ID)
Note

Funding Agencies:

Faculty of Science and Agriculture, Swedish University of Agricultural Sciences 

Carl Tryggers Foundation 

Available from: 2016-09-15 Created: 2016-09-15 Last updated: 2017-11-21Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0866-8710

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